1. Technical Field
The invention relates to a resource indication format for an enhanced multicast and broadcast service (E-MBS) in IEEE 802.16m, and particularly, relates to a resource allocation method and a resource indication method for the E-MBS system, and a mobile station using the same.
2. Related Art
FIG. 1A illustrates an enhanced multicast and broadcast service (E-MBS) system. In an orthogonal frequency division multiple access (OFDMA) system such as IEEE 802.16m system, the E-MBS data are allocated in a pre-defined time-frequency region. Referring to FIG. 1A, in the E-MBS system 10, an E-MBS zone such as an E-MBS Zone 1 in FIG. 1A consists of multiple base stations (BSs), which can transmit the same data to a group of terminals or mobile stations (MSs) within the coverage of the E-MBS Zone 1. The base station BS1 transmits a first set of E-MBS flows to MSs within the coverage of the base station BS1. Another E-MBS Zone 2 also consists of multiple base stations (BSs) transmitting another set of data to a group of terminals or MSs within the coverage of the E-MBS Zone 2. The base station BS3 transmits a first set of E-MBS flows to MSs within the coverage of the base station BS3.
However, there may be multiple service flows for an E-MBS Zone such as the base station BS2 as shown in FIG. 1A. A base station can belong to multiple E-MBS zone such as the overlapping situation shown in FIG. 1A, where the base station BS2 is located in an intersection of the E-MBS Zone 1 and the E-MBS Zone 2. The base station BS2 can simultaneously transmit the first set of E-MBS flows and the second set of E-MBS flows to MSs within its coverage. The base station BS2 belongs to both the E-MBS Zone 1 and E-MBS Zone 2. To be more specific, an E-MBS Zone can be described as a set of BSs or Advanced BSs (ABS) where the same E-MBS identifier (ID) and flow IDs are used for transmitting the content of certain service flows. Here, the service flows can be, for example, video program or audio program. Also, the service flows can be broadcast, multicast or even unicast to MSs. On the other hand, an E-MBS region is a two-dimensional time-frequency resource for the E-MBS in the downlink.
FIG. 1B is a schematic diagram illustrating E-MBS data allocated in pre-defined time-frequency regions. Referring to both FIG. 1A and FIG. 1B, E-MBS region 1 is the time-frequency resource allocated for the E-MBS zone 1 and E-MBS region 2 is the time-frequency resource allocated for the E-MBS zone 2. The base station BS2 transmits OFDM time-frequency resource including both the E-MBS region 1 and the E-MBS region 2. In the two-dimensional time-frequency resource for the E-MBS illustrated in FIG. 1B, the vertical axis is in frequency domain which includes multiple subbands, and each one of the subbands includes, for example, 4 resource units in frequency domain. Also, each one of the resource units includes, for example, 18 subcarriers. On the other hand, the horizontal axis in FIG. 1B is in time domain, which includes multiple frames, and each one of the frames can include multiple subframes. The total OFDM time-frequency resource, for example, can be allocated a 10 MHz bandwidth, and each one of the frames can be, for example, 5 milliseconds.
In the IEEE 802.16m system, the minimum downlink (DL) resource allocation is an physical resource unit (PRU), which consists of Psc consecutive subcarriers by Nsym consecutive symbols in time domain. Nsym is the number of symbols of a subframe. In addition, 4 PRUs form a subband in frequency domain.
An E-MBS zone is defined as the coverage of multiple BSs that transmit the same multicast or broadcast data. The BSs in the same E-MBS zone are allocated an identical time-frequency region transmitting the same data. The region allocation parameters are specified by BS control channel. For example, In the E-MBS Zone 1, the base station BS2 can transmit multiple service flows, which are distinguished by different flow IDs. The E-MBS MAP in the IEEE 802.16 standard, at the beginning of the E-MBS region 1, includes the flow ID and the resource allocation information for each one of the service flows in this E-MBS zone 1. The terminals or MSs, which are intended to decode multicast/broadcast data in this E-MBS zone 1, must decode the A-MAP to find out the location of a specific service flow in the E-MBS region according to the flow ID and the resource indication for each one of the service flows.
The conventional approach of indicating resource for each one of the service flows based on IEEE 802.16-2009 frame is to allocate a complete rectangular E-MBS region containing several service flows which are configured in MAC layer. The rectangular E-MBS region is indicated by four parameters such as a two-dimensional left-upper corner (both time offset and frequency offset), the width of the rectangular B-MBS region (the number of symbols) and the length of the E-MBS region (the number of subbands or subchannels). The aforementioned conventional approach in fact wastes resource. Therefore, it is an important issue to find an effective and efficient resource indication format and resource indication scheme so as to enhance E-MBS system performance.